As a mechanism to carry information over long distances, store-and-forward (S&F) networks offer an efficient, low-cost alternative to the existing public switched telephone network (PSTN). In general, S&F networks operate parallel to, and are accessed by, the PSTN.
FIG. 1 shows schematically PSTN 14 and S&F network 22 connected in parallel between a source fax machine 10 and a destination fax machine 30. An autodialer 12, positioned between the source fax machine and PSTN 14, designates incoming faxes for transmission over either the PSTN 14 or S&F network 22. If for example the destination of the incoming fax is not one serviced by the S&F network, then the autodialer dials the destination telephone number directly to the local exchange 16; the call is then carried in a normal fashion by the PSTN 14 to the destination fax machine 30. In contrast, if the number is one serviced by the S&F network, the autodialer dials the telephone number corresponding to that of the source network node 24. The local exchange 16 then routes the call through the PSTN to the source node. (Note that, depending upon their proximity, the source fax machine 10 and the source network node 24 may be served by the same or different local exchanges.) Once it has completely received the document, the source node 24 transfers it to the destination network node 28 over dedicated circuit 26. At this point, the destination node 28 dials the destination telephone number to its local exchange which in turn transfers the call via the PSTN to the local exchange 20 and then to destination fax machine 30. (Note again that, depending upon their proximity, the destination fax machine 30 and the destination network node 28 may be served by the same or different local exchanges.)
In summary, transport of information from the source fax machine to the destination fax machine using the S&F network requires three distinct steps:
(1) from the source fax machine to the source network node via the PSTN; PA1 (2) from the source node to the destination node via dedicated circuits; and PA1 (3) from the destination node to the destination fax machine, again via the PSTN.
Store-and-forward networks offer a number of significant advantages over standard telephone networks for transport of facsimile. For example, a fax document can be carried 15 times more efficiently using packet technology employed by S&F networks. A common annoyance in telephony is the inability to complete a call, usually because the destination device is busy or does not answer. Although sophisiticated voice mail systems have been designated to overcome this problem in voice telephony, similar practical and cost effective solutions do not exist for fax. S&F networks offer a viable solution. A properly implemented S&F network will employ a sufficiently large number of telephone circuits such that a customer fax machine never encounters a busy signal. At the destination end, it is a common practice to design into S&F networks the ability to automatically redial those call attempts which encounter "busy" or "no-answer" signals. Normally, the calls are redialed periodically over a fixed interval of time, every ten minutes for a half hour, for example.
Since multiple messages are typically coursing through an S&F network at any point in time, it is important to have some mechanism to monitor the location and status of each. For example, in one known S&F network, a small data file called an envelope is created to track each fax document as it moves through the network. The source node creates the envelope after it receives an incoming fax document. As the fax document moves through the network, the envelope moves between the network devices and receives continuous updates regarding the status of the fax. This enables substantially real-time monitoring of the fax delivery process.
In the known S&F network, upon concluding the delivery attempt process, the destination network node declares the fax document either "delivered" or "not delivered"; it records the status in the corresponding envelope which is then returned to the source node. If the delivery was successful, the envelope is forwarded to an historical database (HD) which provides a basis for constructing customer bills. If the delivery was not successful, the envelope will be forwarded to a delivery assist system (DAS) for further processing. DAS is a database management system which provides a human operator, the document delivery analyst, with the delivery history and options for resubmission to the network of the document in question. One of the possible actions the analyst may take is to assign the fax to an alternate destination number, one that has been prearranged with either the sender or the receiver.
It is, of course, possible to ask the customer (source) of a given fax document for alternate delivery instructions, either before or after a problem is encountered with delivering a fax. However, obtaining alternate delivery instructions from a customer for every possible destination number is very time-consuming for both the customer and network provider; more importantly, it is likely to decrease the customer's perceived benefit of utilizing the S&F network. A request (to the customer) for alternate delivery information can certainly be postponed until a problem is encountered with a given destination number. This, however, may have the undesirable consequence of introducing a substantial delay before the document can be delivered, thus significantly degrading the guarantee of timely delivery offered by the network provider. Thus, there is a need for some means of obtaining alternate delivery information without alienating the customer or significantly delaying his otherwise undeliverable fax.